The conventional refining of lead results in the concentration of antimony and other elements, usually as oxides in the refining dross or slag, separable from the refined lead bullion. These elements, along with considerable amounts of lead, present as oxides in the refining drosses, are of value and are normally recovered.
The conventional method used to recover lead, antimony and other elements present in the refining drosses usually includes processing these drosses through a smelting operation. Typically, such smelting operation utilizes a blast furnace where the refining drosses and other lead bearing materials are first mixed with coke, limestone and iron and charged into the furnace. At smelting temperatures of 2000.degree. to 2500.degree. F. (1121.degree. to 1371.degree. C.), the lead bearing materials are smelted and the oxides are reduced by the coke to produce metallic lead bullion containing most of the other valuable elements from the refining drosses. The limestone and iron serve as flux to form a slag substantially void of lead and other elements of value.
The recovered lead, including the other elements of value recovered therein, is further utilized in refining processes to make desired alloys. During this further refining process, any undesirable elements present are again oxidized and form refining drosses which are recycled through the smelting operation to recover the lead and the other elements. The recycling of the dross, containing undesired alloying elements, is usually continued until the amount of dross and the processing thereof become uneconomical to process further. The dross is then removed and stored until the alloying elements therein are needed for making desired alloys or is otherwise disposed of which may incur substantial expenses. This entire dross recycling operation is costly and the cost increases proportionately with the number of cycles involved.
In another method, as taught by Hanak in U.S. Pat. No. 1,786,906, an alkali metal process is used to form a slag consisting of caustic soda-sodium antimony alloy melt. To recover the antimony, the slag is cooled and treated with water to dissolve the caustic soda and react with the sodium in the sodium antimony compound to form the hydroxide. The antimony is liberated in the metallic state. The caustic solution is decanted, filtered, evaporated and recovered as dry caustic soda for reuse.
In another process, the recovery of metals from semifinished lead refinery products is described in Pr. Inst. Met. Niezelaz, 1973, 2(4), 175-81 (Pol). Indium, tin and antimony are recovered from dross, obtained during the first stage of lead smelting, of the composition lead 70, copper 3.14, zinc 8.4, tin 1.7, antimony 1.0, arsenic 0.45, [sic] zinc 0.04, and silver 0.015%. The dross is melted at 1213.degree.-1372.degree. K. (1724.degree. F., 940.degree. C.-2010.degree. F., 1099.degree. C.) with 6% coke and 6% Na.sub.2 CO.sub.3 flux. The lead is refined with 5% KOH and 2% KNO.sub.3 at 693.degree.-723.degree. K. (788.degree. F., 420.degree. C.-842.degree. F., 450.degree. C.) and the slag is leached alternately with alkali and acid. It is possible to recover 68% indium, 73% tin and 75% antimony.
All of the above prior art processes have shortcomings in that they are highly inefficient either in materials utilization and/or time (labor) and energy consumption as compared with the process of the present invention which recovers substantial amounts of lead, antimony and other elements contained in the refining dross, incurring significantly less material, labor and fuel costs.